An investigation of friction mechanisms of paper-to-paper friction of coated papers

Abstract Different friction mechanisms for coated board were investigated. Friction due to adhesive forces, interlocking of asperities and plastic deformation, respectively, was evaluated for coated board. The measurements of friction were combined with measurements of surface energy and measurements of gloss variations. The samples coated with only latex showed significant frictional forces but no signs of polishing or plastic deformation. Friction seemed here to depend on adhesive forces and a correlation could be observed between the surface energy and the coefficients of friction. Adhesive forces seemed to be of less importance for coatings with normal binder content. Increases in gloss variations indicated that friction was partly due to plastic deformation resulting from polishing. Samples calendered at room temperature showed clear signs of polishing while samples calendered at increased temperatures showed little or no polishing. These samples were probably too smooth on a particle level to create wear on each other during friction measurements. The base substrate, on the other hand, did not seem to have any influence on friction, and it was thus concluded that friction depended mostly on asperities on a particle size scale and plastic deformation due to polishing.